In general, detergent compositions contain ordinary anionic surfactants as the main component together with higher fatty acids (in the case of skin cleansers) or higher alcohol sulfate salts or polyoxyethylene higher alcohol sulfate salts (in the case of hair shampoos). However, these ordinary surfactants have various disadvantages. For example, a detergent containing higher fatty acids frequently causes the formation of scum (calcium salts of higher fatty acids) upon rinsing. Further, such a detergent is insufficient in foaming power or sustained foaming. On the other hand, higher alcohol sulfate salts are poor in foam breakage or cannot give a smooth feel to the shampooed hair.
Inorganic or organic salts of N-long chain acyl amino acids, which are excellent not only in surface activity but also in bactericidal action, have been widely employed in recent years. It is known that detergents containing these components have a high detergency and exert mild actions on the skin. For example, JP-A-50-150701 and JP-A-63-2962 disclose low-irritative liquid detergents containing N-long chain acyl amino acid surfactants as basic ingredients while JP-A-53-132007 discloses an improved solid detergent containing an N-long chain acyl neutral amino acid (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
Although the tertiary amide-type N-long chain acyl amino acid salts employed in the detergents disclosed in these patents are highly soluble in water, they are poor in foaming power and foam breakage. In addition, they give a slimy feel at the use.
On the other hand, a secondary amide-type N-long chain acyl amino acid salt is described as a low irritancy surfactant in an Example in JP-A-63-2962. According to this Example, however, satisfactory effects cannot be achieved thereby. Further, a detergent composition containing the secondary amide-type N-long chain acyl amino acid salt alone as a base scarcely shows a satisfactory foaming power or sustained foaming and gives a good feel at the use.